Photosensitive device



E. D. WILSON PHOTOSENSITIVE DEVICE Filed Jan. 31, 1935 Oct. 12, 1937.

4a Fooz Candles.

INVENTOR Earl D. Wilson.

'2o Fool" Candles.

Patented oci. 12, 1937 UN if PHOTOSENSITIVE DEVICE Earl D. Wilson,Wilkinsbnrg, Pa., assignor to Westinghouse Electric & ManufacturingCompany, East Pittsburgh, Pa., a corporation of Pennsylvania ApplicationJanuary 3l, 1935, Serial No. 4,2875

2 Claims.

This application is a continuation in part of my copending application,Serial No. 578,399, filed December 1, 1931 for Photo-sensitive devices.

My invention relates to photo-sensitive devices and has particularrelatio-n to photo-sensitive devices of the dry photo-voltaic type.

Photo-voltaic cells constructed and operated according to the teachingsof the prior art, of which I am aware, are of several types. One type ofcell well known in the art comprises a copper disc having disposedthereon a layer of copperoxide transparent to ordinary light radiations.Contact is made with the copper oxide through a grid, preferably ofspiral structure, that is rigidly clamped against the oxide surface.

In such a cell the photo-electric effect apparently takes place on theinner surface of the copper oxide, that is to say, at the interfacebetween the pure copper surface'. and the oxide surface. The light isevidently transmitted through the copper oxide and its effect isevidenced by a flow of an electron current from the copper oxide to thecopper or a flow of a conventional current from the copper to the copperoxide.

Another type of cell which is well known in the art comprises a solidplate of cuprous oxide which is produced by converting a copper metalplate completely to the oxide by suflicient baking. On one surface ofthis plate a translucent lm of metal is disposed. Contact is made withthe lm of metal on one surface and with a conducting layer of materialsprayed on the other surface oi the copper oxide, and when the unit issubjected to the influence of illumination, an electron current ilowsfrom the copper oxide to the translucent film of metal.

In experimenting with these cells I have found that the current whichflows in the last-named oxide disc which, of necessity, must receiverather careful treatment, is an expensive unit, and for this reason isnot at all adaptable to the ordinary commercial uses to which thephoto-voltaic cell is, at the present time, applied. My experiments alsohave lead me to the conclusion that, in general, the electron emissionexcited by light energy in the cells of the photo-voltaic type' takesplace by reason of some property of the copper oxide and the electronsare emitted by the copper i oxide. YThe direction of emission and itsmagnitude are probably dependent on the Surface which the light impingesand is absorbed, on the magnitude of the impinging illumination and onthe intimacy of the contact between the absorbing surface and itsjuxtaposed conductor.

It has been the practice in the art to designate the photo-electric eectwhich is attained when the current ows'frorn the photo-sensitivematerial to its metallic backing as the reverse effect and the eectwhich is attained when the electron current flows from thephoto-sensitive material to the contacting film as the obverse effect.Applying these designations to the conclusions of the discussions givenhereinabove it appears that, in general, the obverse effect isconsiderably more marked than the reverse effect.

It is an object of my invention to provide an inexpensive photo-cell ofthe photo-voltaic type wherein the electron current shall flow away fromthe metal on which the photo-sensitive material is deposited.

Another object of my invention is to provide a photo-voltaicphoto-sensitive element that shall be inexpensive to manufacture onlarge quantities of the type wherein the emission, arising by reason ofimpinging radiations, takes place from the surface of th photo-sensitivematerial facing the source of radiation.

Still another objectA of my invention is to provide an inexpensiveprocess for preparing a photo-voltaic cell of the type wherein theelectron emission takes place from the surface of the material facingthe source of radiation that excites the emission.

A further object of my invention is to provide a simple and inexpensiveprocess for preparing a photo-voltaic cell of the obverse type.

More concisely stated, it is an object of my invention to provide aninexpensive photo-voltaic cell that shall yield considerable power ascompared with the cells of the prior art and that shall be soinexpensive to manufacture on a commercial scale as to be 4capable ofgeneral commercial applicability.

According to my invention, I provide a cell l comprising specifically, acopper plate having deposited thereon a layer'of copper oxide. Thecopper copper-oxide plate is treated in a manner that shall be describedhereinafter and after such treatment it is subjected to a discharge inan atmosphere of a highly rarified argon.V The discharge takes placepreferably between a silver plate and an ordinary electrode and thesilver plate is so disposed relative to the copper-oxide surface of thecopper copper-oxide plate that a Hlm of silveris sputtered on thesurface thereof.

I have found that, when such a unit is con-l nected through a suitablemeter and is subjected to the influence of light, an electron currentflows from the copper oxide to the sputtered silver and is returnedthrough the metal and through the copper to the copper oxide. -Thecurrent is several times as large as the current of opposite polaritywhich ows in the cells of the prior art in which the photo-electriceffect apparently takes place at the interface of the copper and thecopper oxide. On the other hand, the preparation of the unit requiresvery little in the way of skill in operation or elaborate treatment andis, consequently, considerably less expensive than the pure copper-oxideunit provided in accordance with the teachings of the prior art.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of a specificembodiment when read in connection with the accompanying drawing, inwhich:

Figure l is a View partly in perspective and partly in section, showingan embodiment of my invention;

Fig. 2 is a view partly in section and partly diagrammatic showing acomplete cell constructed according to my invention, and provided withthe elements necessary for incorporating it in a closed working circuit;

Fig. 3 is a view in section showing a container wherein my cell istreated in the preparation thereof;

Fig. 4 is a graph showing a series of current illumination curves for acell constructed in accordance with the teachings of my invention; and

Fig. 5 is a graph showing a voltage illumination curve for a cellconstructed according to my invention.

The apparatus shown in Fig. 1 comprises a copper plate I having a layerof copper oxide 3 deposited thereon. In general, the copper copper-oxideplate I may be produced simply by oxidizing one face of an ordinarycopper plate. However, it may be of a structure similar to that utilizedin ordinary rectifying apparatus and may be produced and treated by thesame process as is utilized in the production and treatment of coppercopper-oxide rectiers. As shall be seen hereinafter, it may be ofadvantage to destroy the rectifying property of the plate, but thisobject can be accomplished after the plate is produced. l

On the surface of the copper oxide a thin lm 5 of sputtered metal,preferably silver, is deposited. The lm 5 of metal is so thin as to besubstantially transparent but for certain applications of my invention,a translucent film is suitable.

The layer 3 of copper oxide on the other hand, should preferably be soopaque as to prevent the transmission of light to the interface and thusto prevent the production of an electron current flowing in a directionopposite to the current for which the plate is particularly provided.

In Fig. 2 a photo-cell constructed according to the teachings of myinvention is shown as connected in an electric circuit. The system shownin the view comprises a disc 'I of the type shown The plate, thusprepared, is provided with suitin Fig. 1, having an opening 9 therein.Electrical contact is made with the sputtered metallic film 5 on thesurface of the copper-oxide layer 3 through a washer II which is clampedto the sputtered film 5 by a bolt I3. The bolt I3 passes through theopening 9 in the plate; and its lower threaded surface I5 is engagedlbya nut I'I that, in turn, is so tightened as to engage the lower surfaceof an insulated washer I 9. By the clamping action of the nut I'I andbolt I3 the insulated washer I9 is clamped against the copper surface ofthe photo-sensitive disc 'I while the metallic washer II is clampedagainst the conducting film 5 on the surface 3 of copper oxide.

A lead 2| is soldered to the lower surface of the copper element Iof thedisc 1 while a second lead 23 is firmly secured to the nut I1 thatengages the bolt I3. When the device is utilized simply for themeasurement of illumination, the circuit through the elements of thedisc may be completed througha suitable meter 20. The polarity of theelectromotive force set up by the disc under the iniiuence of light isillustrated by the conventional symbols in Fig. 2.

'Ihe light passes through the lm 5 and strikes the copper oxide surface3. Electrons are released from the copper oxide surface and travel tothe film 5. This electron flow makes the film 5 negative according tothe accepted current and potential designation and the copper oxide"positive. 'I'he electron flow, in the type of device in Fig. 2, is fromthe film 5, washer II, bolt I3. lead 23, meter 20, lead 2|, copper I tothe oxide 3.

According to my researches, the photo-sensitive plate 'I may be bestprovided by suitably treating a copper disc of which one surface hasbeen oxidized. I have found that after the surface is oxidized, the discshould be subjected to several mechanical impulses of considerablemagnitude. This object can best be accomplished by depositing the plateon a table placing a wooden block on top of it and hammering the blocksubstantially with an ordinary hammer.

While I 'am not certain as to the theoretical reasons for theimprovement which is attained by hammering the plate, my conjecture isthat by such treatment the tendency of the plate to produce an electroncurrent fiowing from the copper oxide to the copper base is destroyed.It has been found that hammering destroys the rectifying property of acopper copper-oxide disc, and according to present theories, there is adefinite relation between the photo-electric property of a coppercopper-oxide disc and its rectifying property.

After having been subjected to the mechanical impulses the plate isalternately dipped into an acid bath and into flowing water until theoxide acquires a glassy cherry red surface. The bath may be preferablyconcentrated nitric acid. After the plate assumesvthe proper appearanceas described hereinabove, it is thoroughly rinsed and dried, care beingtaken at the same time, not to deposit any foreign material on itssurfaces.

The sputtered film is deposited on the plate in a container 25 equippedwith an outlet 26 whereby it may be exhausted. The copper copper-oxideplate is mounted'on a stopper 21 provided with a ground surface toengage the ground internal boundary 29 of a conoidal-shaped opening inthe container 25.

The copper copper-oxide disc is rigidly secured to a heavy copper block3I that is, in turn, fastened to a plurality of rods 33 welded in a stem35 projecting from the stopper 21 for the con- Cil tainer 25. Inpractice, it is desirable that the edges of the disc shall not besputtered and I have provided a suitable mask 31 that is mounted on thecopper coppereoxide disc after the latter is secured to the copper block3|. The block 3l is of such size that the copper copper-oxide disc isprevented from becoming hot when subjected to the influence of thesputtering apparatus.

A silver plate 39 is disposed parallel to the copperoxide surface 3 ofthe disc and at a short distance therefrom. A lead 4l suitably welded inthe walls of the container 25 is connected to the plate 39 and providesa suitable connection to a power supply source f not shown).

The electrode cooperating with the silver plate 39 is preferably acollar 43 suitably mounted on a constricted portion 45 of the stopper 21provided for the container 25. A lead 41 connected to the collar 43 andwelded to the walls of the stopper 21 provides for the connection of thepower supply source to the collar. l

In the practice of my invention the container 25 is completely exhaustedand then filled with argon at a low pressure. My investigations havelead me to the conclusion that for the most desirable results thecontainer 25 must be first evacuated as completely as possible. Thepressure of the argon should be from .4 to .5 millimeters of mercury.This pressure may be measured if desirable with an ordinary gage.However, I have found that for all practical purposes the pressure maybe suitably estimated by noting the character of the discharge throughthe gas.

After the container has been completely exhausted and suitably filledwith the raried argon, the collar 43 is then connected to the positiveterminal of an approximately '150 volt power source while the silverplate 39 is connected to the negative terminal thereof. A discharge isthus produced in the container and is continued for fifteen seconds`after which it is found when the disc is removed from the block 3|, thata thin layer 5 of silver has become sputtered on the surface 3 of Vthecopper oxide.

In Figs. 4 and 5 graphs are shown giving the general characteristics ofa photo-cell constructed according to my invention. In Fig. 4 thecurrent transmitted by a cell in mi-lliamperes is plotted as ordinate,while the light flux impinging on the cell in foot candles is plotted asabscssa.

As will be noted in Fig. 4, a family of curves 49, 5l, 53 and 55 isplotted. The parameter for the curves is the resistance connected in thecircuit with the cell 1. The four resistances utilized in taking thecurves 49, 5|, 53 and 55 shown in the view were respectively 1 ohm, 1lohms, 100 ohms and 1000 ohms.

In Fig. 5, the voltage output of a cell constructed according to myinvention in milli-volts is plotted as ordinate and the light fluximpinging on the cell in foot candles is plotted as abscissa.

The curve 51 shows the characteristic of an average cell. y.

In discussing the features of my invention I have referred hereinabove,in general, to a photocell of the copper copper-oxide type. While myinvention is specifically applicable to a cell of this type, a number ofthe features discussed herein are equally as well applicable tophoto-voltaic cells of other types, such, for example, as the cell madeup of an iron plate, a selenide deposited on the plate and a silverdeposit on the selenide layer. To the extent to which my inventionapplies to cells of other types, it is understood that the applicationsof my invention to such cells are equivalents which lie within the scopethereof.

Again while discussing the elements of my invention, I have referred, ingeneral. to silver as the preferable contacting material to be utilizedlwith the copper copper-oxide disc. While I have found that silver yieldshighly satisfactory results, it is possible that other metals may existwhich would yield as satisfactory results, or which would be applicablefor cells utilized for a particular purpose. These other metals are,particularly, gold and platinum that form with silver the group of noblemetals that have a very high conductivity even in the thin substantiallytransparent film as described in connection with my photo-electricdevices. These metals add the desired photoelectric effect incombination with the copper oxide, and yet withstand undesirablechemical action and, accordingly, protect the photo-sensitve device, inaddition to their photo-electric effect. If gold is used, this gold hasthe advantage that it readily passes the green portion of the spectrumto which the human eye is most sensitive and, accordingly, a cell withthe gold layer as the photo-active material in combination with thecopper oxide, will have a color sensitivity comparable with that of thehuman eye. My invention is, therefore, not to be restricted to a cellincorporating only a silver contacting surface.

Although I have shown and describedcertain specific embodiments of myinvention, I am fully aware that many modifications thereof. arepossible. My invention, therefore, is not to be restricted exceptinsofar as is necessitated by the prior art and by the spirit of theappended claims.

I claim as my invention:

l. As an article of manufacture, a photo-sensitive device comprising anopaque copper plate, an opaque layer of copper oxide formed on at leastone surface thereof and `a translucent layer of metal in intimatecontact with said layer of copper oxide.

2. As an article of manufacture, a photo-sensitive device comprisingopaque copper having an opaque layer of copper oxide on atleast aportion of the surface thereof and a translucent metallic layer on saidlayer of copper oxide.

EARL D. WILSON.

